Fig. 75 Sphacelaria. A, plant of 5. cirrhosa ( x ^). B, apical cell (a) 

 of 5. cirrhosa. C, 5. cirrhosa, origin of hair (h). a = apical cell. D, 

 hair at older stage; a = apical cell. E, apex of thallus of S. plumigera 

 showing branches, 6; single segment (5), which later divides into 

 upper {us) and lower (Is) segments; a = apical cell. F, origin of 

 branch, h. G, bulbil of S. cirrhosa ( x 52-5). H, unilocular spor- 

 angia, S. racemosa. I, zoospore of 5. bipinnata ( x 1200). J, K, ger- 

 minating spore of 5. bipinnata ( x 1200). (A, original; B-G, after 

 Oltmanns; H, after Taylor; I-K, after Papenfuss.) 



modified branches or propagules which vary in shape from wedge- 

 Uke to di- or triradiate with long or short pedicels. Unilocular and 

 plurilocular sporangia are borne terminally or laterally on simple 

 or branched laterals and are either sessile or shortly pedicellate. 

 The life cycle of Sphacelaria bipinnata has been worked out in some 

 detail and is probably typical of the genus. 



The asexual generation bears both uni- and plurilocular spor- 

 angia. Zooids from the former fuse in clumps, but those from the 

 latter germinate directly and represent a means of accessory repro- 

 duction. The cytology of the clumps has not been studied though 

 meiosis occurs in the unilocular sporangia. These clumps must 

 give rise to the isomorphic sexual generation which reproduces by 

 means of isogametes liberated from plurilocular sporangia. 



K 137 



